Megacity ozone air quality under four alternative future scenarios 1Max Planck Institute for Chemistry, Mainz, Germany
16 May 2012
2Institute for Advanced Sustainability Studies, Potsdam, Germany
3Centre for Atmospheric Science, Department of Chemistry, Cambridge University, UK
4NCAS Climate, UK
5TNO – Department Climate, Air and Sustainability , Princetonlaan 6, 3584 CB Utrecht, The Netherlands
Received: 25 November 2011 – Published in Atmos. Chem. Phys. Discuss.: 02 January 2012 Abstract. The impact of the megacities of the world on global tropospheric ozone, and conversely,
the extent to which
megacities are influenced by emissions of ozone precursors from outside of the megacities
is examined under the four
alternative RCP ("Representative Concentration Pathway") emissions scenarios.
Despite accounting for about 6% of present-day anthropogenic emissions of ozone precursor species,
the contribution of emissions from megacities to global tropospheric ozone is calculated to be 0.84%.
By 2100 this contribution falls to between 0.18% and 0.62% depending on the scenario,
with the lower value being for the most-polluting of the four future emissions scenarios
due to stringent controls on ozone precursor emissions from highly populated
areas combined with a
stronger tropospheric background ozone field.
The higher end of this range is from the least-polluting of the four emissions scenarios,
due to lower background tropospheric ozone combined with the use of a simpler downscaling
methodology in the construction of the scenario, which results in higher emissions from
Although the absolute impact of megacities on global ozone is small, an important result of this
study is that under all future scenarios,
future air quality in megacities is expected to be less influenced by local emissions
within the cities, but instead more influenced by emission sources outside of the cities,
with mixing ratios of background ozone projected to play an increasing role in megacity air quality
throughout the 21st century.
Assumptions made when downscaling the emissions scenarios onto the grids used in
such modelling studies can have a large influence on these results;
future generations of emissions scenarios should include spatially explicit representations
or urban development suitable for air quality studies using global chemical transport models.
Revised: 25 April 2012 – Accepted: 04 May 2012 – Published: 16 May 2012
Citation: Butler, T. M., Stock, Z. S., Russo, M. R., Denier van der Gon, H. A. C., and Lawrence, M. G.: Megacity ozone air quality under four alternative future scenarios, Atmos. Chem. Phys., 12, 4413-4428, doi:10.5194/acp-12-4413-2012, 2012.